Inflatable support

ABSTRACT

A support surface  10  includes a series of inflatable cells  30, 40  inflated alternately by a compressor  11.  The cells  30, 40  are exhausted via an exhaust port  50  having a restrictor  60  of known diameter. A pressure transducer  70  measures the cell  30, 40  pressure. Some of the cells  30, 40  during their deflating/inflating cycle are exhausted through the exhaust port  50  and the cell pressure decay over a time is monitored. A microprocessor calculates the mathematical function related to the cell pressure decay with time, compares the value with compiled data and adjusts the output of the compressor accordingly. The sequence of exhausting via port  50  is repeated at every inflation/deflation cycle and the pressure decay monitored and compared with the known data and the compressor output adjusted automatically to provide a new operating pressure. Therefore, any changes in the person&#39;s position i.e. supine, to side or sitting are accomodated by the cell pressure automatically being adjusted to prevent bottoming or high interface pressures.

[0001] The invention relates to an inflatable support for the preventionand treatment of pressure sores.

[0002] Pressure sores are a condition of progressive tissue death causedprimarily by the combination of pressure and shear forces on the humanbody particularly in the regions of the bony prominences' such asischials, trochanter and heels. These forces act by reducing or stoppingthe microcirculatory function bringing fresh nutrients (includingoxygen) to and removing waste products from the soft tissues underlyingthe skin. Pressure sores are always debilitating, can often be fatal andeven with optimum intervention take from weeks to months to completelyheal. The resulting costs for a developed nation (including NATRA, EU,Australasia, Japan) range from £100 m to £600 m annually.

[0003] Pressure relieving or reducing supports are provided both inmattress form for lying on and seat product form supporting the buttocksand sometimes the back in operation. All of these support products usedifferent technologies but can be put into two categories by the waythey deal with the problem of lowering the pressures imposed on thevulnerable bony prominences (which are at highest risk of pressuresores) by supporting the weight of the human body.

[0004] These pressures must be reduced below those that compromise orstop altogether the functions of the capillary bed of themicrocirculation in delivering nutrients and removing waste products.For a healthy person this is approximately 32 mmHg but at the capillarybed exits the pressure can be as low as 12-14 mmHg for some persons.

[0005] Pressure reducing products work by moulding themselves around theshape of that part of the human body in contact with them, creating thelargest contact area and therefore lowering the contact pressures. Thetechnologies used include foam, static air filled bags, gel filled bags,water mattresses and waterbeds. These may be used alone or incombination and include fluidising fine silica beads to create a liquidlike substance supporting the body by Archimedes principle of upthrustand displacement balance used for burns patients.

[0006] However typical human skin area is 1.8 m2 and in a supine backlying position at most half of this could be contact area so this limitsthe ultimate pressure reduction.

[0007] The alternative concept is that of pressure relief where the partof the body in contact with the mattress or seating product is supportedonly partially with the contact points being removed in location overtime by raising and lowering each part of the product in a predeterminedsequence. This principle is invariably implemented using air to inflateor deflate bladders called cells within the product in the predeterminedsequence required. Such products are commonly referred to as alternatingair products. These static or alternating air based pressure soremattress and seating products form the largest and most clinicallyeffective (in alternating form) part of all such products.

[0008] The pressures imposed by an air mattress on the body are calledinterface pressures and are a function of the internal or operatingpressure of the system. If internal pressure is too low than the partsof body supported touch the base below. But too high a pressure andpressure sores may develop. The majority of people associate lowerpressures with more comfort. Patient perception of comfort is importantto obtain high compliance and optimum sleep patterns for faster healing.

[0009] It is known that operating pressure has to be optimised for anindividual patient and is dependent on spatial distribution of patientbody density over the area in contact with the mattress or seatingproduct and varies with each patient and their position on the mattress.

[0010] Because the bodies' average density varies considerably betweentrunk (low average density) and other parts such as heels (high averagedensity) many air products are divided into separate sections or zoneseach with a different operating pressure.

[0011] In order to get optimum pressure reduction or relief, a number ofsuch products, even multi-zoned, use manual operating pressure settingsrelying entirely on the user or carer for appropriate adjustment.

[0012] However, manual operating pressure control raises many problems,namely, it is labour intensive within the hospital, it is not practicalin nursing homes and particularly homecare as there are no trained staffpresent and may be vulnerable to inadvertent mis-setting to ineffectiveor unsafe positions. Furthermore, apart from gap setting (see below)there is no guide to the right value to guarantee no bottoming andbalance good clinical efficacy with acceptable comfort to the patient.

[0013] Gap setting adjustment involves setting operating pressure to getclearance of two or three fingers width or palm thickness between thelowest part of the patients body and the mattress or seat base. This isphysically intrusive for the patient and difficult or impossible withmost mattress designs due to obstructions of parts of the inflatedstructure.

[0014] Some alternating systems provide semi-automatic operatingpressure setting by means of additional sensors either under themattress or within the mattress to indicate when the patient is at riskof bottoming and to control the pump to re-inflate the mattress.

[0015] However, such systems do not accommodate different positions ofthe patient on the mattress, are complex and still require the user toset the initial operating pressure upon first use. Static systems areknown which upon setting of an operating pressure will then maintain thedesirable operating pressure dependent on the users weight by using lookup tables and pressure sensors sensing and adjusting the internalpressure of the mattress. As with the alternating systems, such systemsstill require the initial pressure to be set by the carer or user.

[0016] It is an object of the invention to provide a simple system thatremoves the need for manual control of the operating pressure ofalternating air mattresses or static systems and automatically set thecorrect operating pressure upon use by the user and more importantlyreset the operating pressure and maintain the same dependent on changeof position of the user or mattress.

[0017] Accordingly, the invention provides an inflatable support for auser comprising one or more inflatable cells inflated with fluid from asource to a set pressure, means for venting at least one cell through aknown restrictor and measuring the pressure change over time, controlmeans converting this pressure change time value into a mathematicalcoefficient and comparing with known experimental data, and selectingthe optimum support pressure and adjusting the source output to providethe optimum support pressure.

[0018] The advantage of the invention is that it uses existing cell airand pressure sensors without adding any components into the mattress.There are no sensors in the mattress, thereby any inflatable mattress isavailable for use.

[0019] Preferably, the cell(s) are vented once every cycle of inflationand deflation in an alternating system for continuous monitoring andresetting of the optimum support pressure.

[0020] In a preferred embodiment, the means for venting at least one ofthe cells is actuated during the deflation cycle. Alternatively, theventing means may be actuated during the inflation cycle.

[0021] Preferably, the cell air is vented through a series ofrestrictors, or more preferably a variable restrictor.

[0022] Preferably, the control means includes compiled experimental dataof pressure decay with time and associated mathematical coefficient forlarge number of users with different body anatomy, on differentmattresses and cushions and with differing initial set pressures. Morepreferably, the control means adds new patient anatomy types andcorresponding mathematical coefficient not present in the knownexperimental data.

[0023] Preferably, the inflatable support may have an additionalanti-bottoming sensor to allow for lower overall operating pressures,for greater user comfort.

[0024] The anti-bottoming sensor may comprise a sensor mat as describedin our European patent No. 560563 and is hereby incorporated byreference.

[0025] In a preferred embodiment the inflatable support may becontrolled by remote means connected to the control means.

[0026] The present invention will now be described in detail, by way ofexample only, with reference to the accompanying drawings in which:

[0027]FIG. 1 is a schematic view of a support surface in accordance withthe present invention;

[0028]FIG. 2 is a schematic view of a support surface 10 according toanother embodiment of the invention; and

[0029]FIG. 3 is a circuit diagram of a remote control device to operatethe support according to the invention.

[0030] Referring now to FIG. 1, a support surface 10 includes a seriesof inflatable cells 30, 40 inflated alternately by a compressor 11 bymeans of either a rotor stator or a solenoid arrangement 20. The cells30, 40 may be exhausted via exhaust port 50, the exhaust portincorporates a restrictor 60 of known diameter. A gauge pressuretransducer 70 measures the cell 30, 40 pressure.

[0031] In use, the support surface is inflated to a set pressure, say 35mmHg. The cells 30, 40 are respectively alternatively inflated anddeflated by means of a rotor stator or solenoid 20 in a cycle typicallylasting 10 minutes. At least some of the cells 30, 40 during theirdeflating cycle are then exhausted through the exhaust port 50 and thecell pressure decay over a time of say 90 seconds is monitored prior tofull deflation of the cells. Thus the impact of loss of pressure in thecells 30, 40 in terms of user comfort is minimal.

[0032] The microprocessor calculates the mathematical function relatedto the cell pressure decay with time, and compares the value with thecompiled experimental mathematical function data and adjusts the outputof the compressor accordingly. These values have been collated byexperiment by measuring cell pressure decay over time from set operatingpressures for different anatomy of users and mattresses. The sequence ofexhausting via port 50 may be repeated at every inflation/deflationcycle and the pressure decay monitored and compared with the known data.Any changes in coefficient values are automatically translated asadjustments in compressor output to provide a new operating pressure. Inthis way, any change in the person's position i.e. lying on their backto their side or sitting are accommodated by the cell pressureautomatically being adjusted to prevent bottoming or high interfacepressures. We have found that the principle works equally if the cellpressure-time relationship is monitored during the inflation cycle ofthe cells 30, 40 instead of deflation, as described above.

[0033]FIG. 2 shows a support surface 10 consisting of inflatable cells100 which are inflated constantly by means of a compressor 130 of knownoutput. A gauge pressure transducer 150 measures the cell pressure inthe fluid lines 160 leading to the cells 100. Similar to the embodimentas described above, the cells are inflated to a set pressure of say 30mmHG and then the cell pressure decay over time through a knownrestrictor is monitored. The value is translated to a mathematicalcoefficient which is compared to similar data compiled within themicroprocessor for such a mattress with different anatomy of users andoperating pressures and the compressor output adjusted to provide anoperating pressure correlating to the coefficient value. Thiscoefficient correlation of the cell pressure change-time relationshipfor a given individual user anatomy and operating pressure has beenfound to be to be consistent in providing optimum support pressure overa wide range to cover all human anatomical variation.

[0034] It is understood that the change in cell pressure monitored viathe transducer in the above embodiments has a direct correlation tochange in flow rates. Therefore monitoring the pressure change to adjustcompressor output may be replaced by monitoring flow rate change may andcompared to the relevant experimental data.

[0035] The invention provides a support surface automatically providingoptimum support pressure taking into account user's anatomy without anyinput from the user.

[0036] This optimum pressure may be made more optimum to provide greatercomfort to the user by having an additional anti-bottoming sensorlocated under the support. A typical anti-bottoming sensor as describedin our European Patent No. 560563 comprises a mat which ensures that thesupport is inflated sufficiently to prevent bottoming of the user i.e.touching the base under the support.

[0037] The user may also be able to control the support comfort by meansof a remote control for adjusting the support pressure, but which wouldnot compromise the therapy set by the carer.

[0038] As shown in FIG. 3, the remote control 80 comprises a simpleseries of switches 81 that can be low voltage, and can be connected inparallel to the membrane control panel and duplicating their operation.

[0039] The switches 81 are connected by a wire to the pump via aconnector 82. The conventional connector 82 could be a telephone jack orsimilar device.

[0040] When a switch 81 is closed a digital signal is seen at theconnector 82 from state O (e.g. OV) to state 1 (e.g. 5V). This signalcan be input into the microcontroller or control system in the pumpinterpreted and the corresponding action taken.

[0041] The remote control 80 is low cost, self powered and physicallyconnected to the pump.

[0042] The connection system 82 further allows connection to a bed frameas the remote control 80 could have switches 81 to adjust bed positionas well as the support comfort control.

1. An inflatable support for a user comprising one or more inflatablecells inflated with fluid from a source to a set pressure, means forventing at least one cell through a known restrictor and measuring thepressure change over time, control means converting this pressure changetime value into a mathematical coefficient and comparing with knownexperimental data, and selecting the optimum support pressure andadjusting the source output to provide the optimum support pressure. 2.An inflatable support as claimed in claim 1 wherein the cell(s) arevented once every cycle of inflation and deflation in an alternatingsystem for continuous monitoring and resetting of the optimum supportpressure.
 3. An inflatable support as claimed in claims 1 or 2 whereinthe means for venting at least one of the cells is actuated during thedeflation cycle.
 4. An inflatable support as claimed in claims 1 or 2wherein the means for venting at least one of the cells is actuatedduring the inflation cycle.
 5. An inflatable support as claimed inclaims 1 to 4 wherein the cell air is vented through a series ofrestrictors.
 6. An inflatable support as claimed in claims 1 to 4wherein the cell air is vented through a variable restrictor.
 7. Aninflatable support as claimed in any preceding claim wherein the controlmeans includes compiled experimental data of pressure decay with timeand associated mathematical coefficient for large number of users withdifferent body anatomy, on different mattresses and cushions and withdiffering initial set pressures.
 8. An inflatable support as claimed inclaim 7 wherein the control means adds new patient anatomy types andcorresponding mathematical coefficient not present in the knownexperimental data.
 9. An inflatable support as claimed in any precedingclaim wherein the inflatable support includes an additionalanti-bottoming sensor to allow for lower overall operating pressures,for greater user comfort.
 10. An inflatable support as claimed in anypreceding claim wherein the inflatable support is controlled by remotemeans connected to the control means.